[Bug c/120636] New: -O3 runtime problems with recent gcc

[dcb314 at hotmail dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=120636

            Bug ID: 120636
           Summary: -O3 runtime problems with recent gcc
           Product: gcc
           Version: 16.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: dcb314 at hotmail dot com
  Target Milestone: ---

Created attachment 61625
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=61625&action=edit
C source code

>From yesterday's compiler:

foundBugs $ ../results.20250610.asan.ubsan/bin/gcc -w -Werror=return-type
-Werror=uninitialized -Werror=overflow -Werror=sequence-point -O3 bug1103.c
foundBugs $ (ulimit -t 60; time valgrind -q ./a.out)
checksum = 2C4CC563

real    0m9.672s
user    0m0.359s
sys     0m0.042s

>From today's compiler with the same flags:

foundBugs $ ../results.20250611.asan.ubsan/bin/gcc -w -Werror=return-type
-Werror=uninitialized -Werror=overflow -Werror=sequence-point -O3 bug1103.c
foundBugs $ (ulimit -t 60; time valgrind -q ./a.out)

real    1m11.622s
user    0m59.860s
sys     0m0.146s
foundBugs $ 

So no results in a time six times longer than with yesterday's compiler.

It is fine at -O2:

foundBugs $ ../results.20250611.asan.ubsan/bin/gcc -w -Werror=return-type
-Werror=uninitialized -Werror=overflow -Werror=sequence-point -O2 bug1103.c
foundBugs $ (ulimit -t 60; time valgrind -q ./a.out)
checksum = 2C4CC563

real    0m0.438s
user    0m0.384s
sys     0m0.035s
foundBugs $ 

Also:

foundBugs $ ../results.20250610.asan.ubsan/bin/gcc -v 2>&1 | grep exp
gcc version 16.0.0 20250610 (experimental) (fce42e15063e76d2) 
foundBugs $ ../results.20250611.asan.ubsan/bin/gcc -v 2>&1 | grep exp
gcc version 16.0.0 20250611 (experimental) (76cbd678d123ed93) 
foundBugs $ 

trunk $ git log fce42e15063e76d2..76cbd678d123ed93 | grep -c "^commit"
60
trunk $